New Boiler Inspection Rules?

According to Steam Railway the return of 257 Squadron has been postponed. It quotes Simon Troy, chairman of SLL, who says: “Whilst the locomotive is ready to steam, further tests to comply with new rulings have been requested by the boiler inspector, so that the locomotive can be passed for insurance purposes. "

I'm intrigued as to what these new rulings are. Can anyone enlighten me?

 

Has someone changed the Red Book without telling us?

 

Change of policy by the Boiler Insurance Company? I don't see why they cannot request higher standards than the legal minimum.

Cheers, Neil

 

Insurance companies can require whatever they like as a condition of insurance. All the ones I've had dealings with simply require that the pressure system complies with the law. The law requires a Competent Person (Boiler Inspector) to carry out a proper inspection and make a report as to whether it is fit for purpose and is likely to remain so until the next examination. The examination is to be in accordance with the written scheme.
My query simply relates to what these new 'rules' are that it is being claimed have to be applied.

 

Has one of the industry pressure vessel codes be updated/reissued recently? I know its not strictly related, but I'd put cash down to say PD5500/ ASMEVIII etc sit on the desks of said competent people, so I speculate that perhaps a revision somewhere in another pressure vessel field has triggered it? I could be speaking p**h...

 

I hope not. These codes are welded PV design codes and have no relevance to examinations of existing riveted boilers.

 

Indeed, however it is well known that seeing as there is no defined steam boiler code, good practice is adopted across the board, drawing from the standards set out in other codes.

 

Bell goes "ding" !

 

A new boiler inspector perhaps? That usually brings new interpretation of rules.

And this is Steam Railway, we know how they like to write headlines...

 

I would say that is more than likily the reason, Or some paperwork wasn't completed correctly and that has meant a new test having to be done?

 

In this case, it's a quote from the email sent to shareholders a week or so ago.

 

Also - what pressure do you test a Bulleid boiler to/beyond? The 280psi they originally ran at, or the later reduced 250psi?

What's the maximum practical pressure for a fire-tube boiler anyway? I've read proposals for modernised/new-build locos with pressures well over 300psi.

 

Many Locomotives in the USA had Boiler pressure of 300 PSI.

 

It is not quite a case of the sky is the limit when it comes to the pressure you can have in a boiler as it is mainly a question of resisting forces until temperature becomes a critical factor. However, what you do with that steam is a different matter. If you are using it in a conventional reciprocating steam engine lubrication and sealing issues will come to the fore at the higher temperatures that come with higher pressures.

 

Slight issue also of maintenance costs rising alongside loco boiler pressure on a logarithmic scale.

 

So if one was to new-build e.g. a Merchant Navy-derived 4-6-4, what implications would there be in running it at 320 or 360psi, assuming the boiler was built sufficiently strong?

 

Weight, for starters - a stronger boiler means heavier (i.e. thicker section plates, more and / or thicker stays etc). Assuming you wanted the extra pressure to allow extra tractive effort, you then get into a need for stronger frames to resist the forces. And even with the extra weight, you might then find the factor of adhesion starts to get a bit low (assuming yo left all other significant dimensions similar).

It's fairly easy to play around with a few numbers in simplistic terms and come up with arbitrarily powerful answers. After a while though you start to realise why the old railway workshops, who had large and experienced design teams, didn't necessarily automatically go down that route - almost every design decision in one area ends up causing problems somewhere else, so that the design process is to try to come up with the best compromise across many factors.

And in any case - it is not as if Merchant Navies running at 250psi historically - or as Clan Line shows, currently - had any problem pulling trains up to 500 tons or more over significantly hilly routes. At which point, the question has to be asked about what benefit a 350psi Merchant Navy would bring. If you use the higher pressure to increase haulage, you find that most stations can still only handle 12 - 14 coach trains anyway; if you use it with smaller cylinders to increase thermal efficiency, you'll never get the design and build costs back in reduced coal consumption.

Tom

 

I'm just thinking of a future main line loco that would be able to do 75-100mph everywhere, when crawling up Shap or Hemerdon or somesuch at sub-50mph will no longer be possible... a MN at 250psi is only making 33,500lb to the 40,000 of the Duchess (despite 7in difference in driving wheel diameter), King, Duke etc.

 

Don't go off the nominal tractive effort figures, they're totally meaningless at 50 mph, and not that accurate at 0 mph.